Ground Cover Supplement : GC Supplement - Summer weeds
12 Issue 137 | Nov – Dec 2018 | GRDC GROUNDCOVER SUPPLEMENT: SUMMER WEEDS GROUNDCOVER WEED ECOLOGY BUTTON GRASS TOXIC TO LIVESTOCK CALTROP IS A NATIONAL THREAT By Dr Catherine Borger n Button grass (Dactyloctenium radulans) is a summer weed species that may provide valuable forage in Western Australia’s summer/autumn feed gap, but it should be grazed with caution as over-grazing can result in nitrate-nitrite toxicity for sheep and cattle. In Queensland, button grass is a problem weed as densities of 10, 26 and 43 plants per square metre reduced mungbean yield by 36, 53 and 69 per cent respectively. GRDC research by the Western Australia Department of Primary Industries and Regional Development (DPIRD) and the University of Queensland is studying button grass ecology to identify management opportunities. Button grass can seed prolifically (up to 15,000 seeds per plant) and generally emerges in summer following rainfall, surviving as long as moisture is available. Where no follow up moisture is available, it is short-lived, setting seed in just six weeks. This means seed produced in early summer can ger minate in late summer or autumn, if there is further rainfall. Initial button grass seed germination ranges from less than five per cent in WA to 30 to 61 per cent in Queensland. Seeds lose their dormancy over a few months as the seed coat degrades. On the soil surface seeds generally ger minate or degrade quickly with five to eight per cent of seed remaining viable after 12 months. However, seed buried at two centimetres or more will not easily ger minate or degrade, with up to 50 per cent remaining viable after 12 months. Therefore, it is more effective to manage button grass in a zero-tillage system where more seeds are left on the soil surface. o GRDC Research Codes UA00149, UA00156 More information: Dr Catherine Borger, WA DPIRD, 0467 816 082, email@example.com; http://grdc.com.au/TT-ButtonGrass By Dr Catherine Borger, Dr Abul Hashem, Dr Bhagirath Chauhan and Dr Sudheesh Manalil n Caltrop (Tribulus terrestris) is emerging as a major summer weed threat across Australia affecting 1.6 million hectares and costing Australian growers $31 million annually. Over two years, with investment from GRDC, researchers at the Western Australian Department of Primary Industries and Regional Development (DPIRD) and the University of Queensland have examined the ecology of caltrop and its impact on crop yields. Long-ter m seed dor mancy makes seed-set prevention vital. When buried at a two or 10-centimetre depth caltrop seed remained viable for more than two years, but on the soil surface ger mination degraded over the same timeframe. Therefore, if most seeds are on the soil surface, as in a pasture, caltrop could be eradicated in two to three years. If mouldboard ploughing is used to bury seed in appropriate soils, seed would need to stay buried for at least 10 years. Caltrop emerges in response to summer rainfall, has a low- lying growth habit and plants are often immature at harvest, making harvest weed seed control impractical. In a summer fallow in WA, caltrop reduced yield of the subsequent winter crop by 10 to 40 per cent, as well as reducing grain protein and increasing screenings. In a summer mungbean crop in Queensland, caltrop densities of four, eight and 15 plants per square metre reduced grain yield by 14, 29 and 33 per cent. o GRDC Research Code UA000156 More information: Dr Catherine Borger, WA DPIRD, 0467 816 082, firstname.lastname@example.org Severe button grass infestation in Queensland reduced mungbean yield by 69 per cent. PHOTO:DRBHAGIRATHCHAUHAN,UNIVERSITYOFQUEENSLANDPHOTO:DRCATHERINEBORGER Caltrop in a summer fallow in Western Australia.
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